Significance: Children with autism spectrum disorder (ASD) demonstrate significant variation in the degree and patterning of core symptomatology as well as high rates of comorbid externalizing behavior problems that can exacerbate impairment in functioning and impede learning. Few factors have been identified as predictive of individual differences in the behavioral phenotype of children with ASD. Innovation: The proposed study builds upon methods that have been successful in understanding individual differences in externalizing problems and clinical symptomatology in children with neurotypical development and other clinical disorders, to elucidate heterogeneity in the presentation of children with ASD. Electrodermal activity (EDA), a measure of sympathetic nervous system activity, is a reliable predictor of externalizing problems in children without ASD, and is related to symptom presentation across multiple clinical disorders. EDA patterns index an individual's fight or fligh response, and these tendencies often interact with the social environment to impart risk and to predict broad functioning. The proposed investigation utilizes new technology that allows for the measurement and modeling of long-term EDA during naturalistic, interactive contexts, and is feasible for use among children with considerable variability in developmental functioning. Project Goal: The proposed study examines EDA as a predictor of externalizing psychopathology and ASD symptomatology in children with ASD (Aim 1), and tests whether these associations are moderated by social factors (Aim 2). Approach: Seventy-five children with ASD between the ages of 6 and 10 years, and their primary caregivers, will participate in a laboratory visit, and parents will complete interviews and questionnaires. Multiple indices of EDA will be measured across structured contexts designed to elicit particular child emotional responses, including compliance situations and mild frustration tasks. We expect that children's EDA profiles will meaningfully predict broad functioning. Specifically, we hypothesize that low EDA arousal will positively predict externalizing psychopathology, including behavioral symptoms as well as formal disorder, whereas greater EDA reactivity will be associated with higher levels of ASD symptoms. Consistent with literature highlighting the importance of the social environment to understanding links between EDA and outcomes, we will test whether harsh and supportive parenting moderate the association between EDA and clinical presentation. Impact: Improved understanding of interactions between children's arousal tendencies and environmental supports will enhance long-term health through tailoring of intervention strategies to reduce challenging behaviors and promote learning readiness in children with ASD. In addition to contributions to clinical science, the proposed study will increase and diversify training opportunities for undergraduate and master's-level students at our designated Hispanic- Serving (HSI) Institution, preparing these students for careers in the biobehavioral sciences.